fix(kernel): Build USB drivers as built-in for live USB boot (ref #39)

Change USB modules from =m to =y for live USB support:
- CONFIG_USB_XHCI_HCD=y (USB 3.0)
- CONFIG_USB_XHCI_PCI=y
- CONFIG_USB_XHCI_PLATFORM=y
- CONFIG_USB_EHCI_HCD=y (USB 2.0)
- CONFIG_USB_EHCI_PCI=y
- CONFIG_USB_OHCI_HCD=y (USB 1.1)
- CONFIG_USB_OHCI_HCD_PCI=y
- CONFIG_USB_STORAGE=y

Required for bootable USB without module dependencies.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

board/mochabin/kernel/config-6.12.85-secubox-led

@@ -7563,24 +7563,24 @@ CONFIG_USB_MON=m
 # USB Host Controller Drivers
 #
 # CONFIG_USB_C67X00_HCD is not set
-CONFIG_USB_XHCI_HCD=m
+CONFIG_USB_XHCI_HCD=y
 # CONFIG_USB_XHCI_DBGCAP is not set
-CONFIG_USB_XHCI_PCI=m
+CONFIG_USB_XHCI_PCI=y
 CONFIG_USB_XHCI_PCI_RENESAS=m
-CONFIG_USB_XHCI_PLATFORM=m
+CONFIG_USB_XHCI_PLATFORM=y
 # CONFIG_USB_XHCI_MVEBU is not set
-CONFIG_USB_EHCI_HCD=m
+CONFIG_USB_EHCI_HCD=y
 CONFIG_USB_EHCI_ROOT_HUB_TT=y
 CONFIG_USB_EHCI_TT_NEWSCHED=y
-CONFIG_USB_EHCI_PCI=m
+CONFIG_USB_EHCI_PCI=y
 CONFIG_USB_EHCI_FSL=m
 CONFIG_USB_EHCI_HCD_ORION=m
 CONFIG_USB_EHCI_HCD_PLATFORM=m
 # CONFIG_USB_OXU210HP_HCD is not set
 # CONFIG_USB_ISP116X_HCD is not set
 # CONFIG_USB_MAX3421_HCD is not set
-CONFIG_USB_OHCI_HCD=m
-CONFIG_USB_OHCI_HCD_PCI=m
+CONFIG_USB_OHCI_HCD=y
+CONFIG_USB_OHCI_HCD_PCI=y
 # CONFIG_USB_OHCI_HCD_SSB is not set
 CONFIG_USB_OHCI_HCD_PLATFORM=m
 # CONFIG_USB_UHCI_HCD is not set
@@ -7605,7 +7605,7 @@ CONFIG_USB_TMC=m
 #
 # also be needed; see USB_STORAGE Help for more info
 #
-CONFIG_USB_STORAGE=m
+CONFIG_USB_STORAGE=y
 # CONFIG_USB_STORAGE_DEBUG is not set
 CONFIG_USB_STORAGE_REALTEK=m
 CONFIG_REALTEK_AUTOPM=y